Support player names and online join flow

Move SignalR group join into GameManager and add support for player names and improved online join flow.

- Moved Groups.AddToGroupAsync call out of GameHubSocket into GameManager (hubContext.Groups.AddToGroupAsync) so group membership is handled when adding players to a game.
- GUI: added player name input to GameJoinMenu and updated JoinGameObject to include playerName and use string gameCode.
- OnlineMode & LocalMode: constructors updated to instantiate games without passing settings; removed WaitingForOpponent state and cleaned up event bindings.
- OnlineGame: rewrote to handle onGameCreated/onGameJoined/onGameStarted/onFieldUpdated/onGameEnded/onError, added joinGame validation (expects 6-digit code), join flow (connect + join), state updates, drop forwarding to player.drop(gameId, index) and place description updates.
- LocalGame: constructor signature simplified to no-arg.

These changes centralize group management, add player identification, validate join codes, and improve game state/event handling for online play.

API/Controllers/GameHubSocket.cs

@@ -42,8 +42,6 @@ public class GameHubSocket(IGameManager gameManager) : Hub
             return;
         }
 
-        await Groups.AddToGroupAsync(Context.ConnectionId, result);
-
         await Clients.Caller.SendAsync("GameJoined", new
         {
             GameId = result,

API/Services/GameManager/GameManager.cs

@@ -3,6 +3,7 @@ using API.Models.DataClasses;
 using API.Models.Game;
 using API.Repository.GameRepo;
 using Microsoft.AspNetCore.SignalR;
+using System.Text.RegularExpressions;
 
 namespace API.Services.GameManager;
 
@@ -27,6 +28,8 @@ public class GameManager(IGameRepository gameRepository, IHubContext<GameHubSock
             return null;
         }
 
+        await hubContext.Groups.AddToGroupAsync(player.ConnectionId, game.Id);
+
         if (game.Players.Count == 2)
         {
             game.StartGame();